1. Field of the Invention
The present invention relates to an ophthalmic apparatus capturing an image of or measuring a subject's eye.
2. Description of the Related Art
Japanese Patent Application Publication No. 62-34530 discusses a fundus camera projecting an alignment index on a cornea of a subject's eye and obtaining a reflected image from the cornea as an alignment image. According to this technique, whether the fundus camera is in an appropriate alignment position is determined based on the focus status of the alignment image.
Japanese Patent Application Publication No. 7-31590 also discusses a fundus camera projecting an alignment index on a cornea of a subject's eye and obtaining a reflected image from the cornea as an alignment image. According to this technique, whether the fundus camera is in an appropriate alignment position is determined based on separation or agreement of the alignment image.
Since the above fundus cameras use singly a single-wavelength light-emitting diode (LED) as a light source for the alignment index, they can determine whether the fundus camera is in an appropriate alignment position, to be sure. However, neither of the fundus cameras can determine whether the fundus camera is positioned close to or far from the subject's eye with respect to an appropriate alignment position. Namely, neither of the fundus cameras can accurately determine the working distance.
Thus, to determine an appropriate direction to move the fundus camera to an appropriate alignment position, the operator first needs to temporarily move the fundus camera closer to or farther away from the subject's eye and next needs to observe whether or not the blur level or the separation level of the alignment image has increased. It is not a problem if the operator moves the fundus camera in an appropriate direction in his/her first attempt. However, movement of the fundus camera in the opposite direction will result in a needless operation.